Constant amplitude zero auto-correlation (CAZAC) sequence has following characteristics:
The module of the amplitude is a constant. For example, the module may be normalized to 1. A zero period auto-correlation. Except for the maximum correlation value with respect to the sequence itself, the sequence has a correlation value of zero with respect to other cyclic shifts.
For a sequence with above characteristics, a sequence in the frequency domain obtained through Fourier transformation is also a CAZAC sequence, i.e. the sequence in the frequency domain also has the characteristics of constant amplitude and zero auto-correlation.
Due to the above characteristics of the CAZAC sequence, much attention is gradually paid to the CAZAC sequence during the design of a communication system. A signal bearing the CAZAC sequence is widely employed in the communication system. For example, in a Single Carrier Frequency Division Multiple Access (SC-FDMA) system, within one symbol time, the sequence is modulated on each sub-carrier for transmission. When the sequence of the transmitted signal is known at a receiver, the receiver may perform channel estimation by use of the received signal. Because the CAZAC sequence has constant amplitude in the time domain, the waveform shows small peak-to-average ratio in the time domain, and is easy to be transmitted by the transmitter.
Meanwhile, because the transmitted signal has the same amplitude on each sub-carrier in the frequency domain, the receiver may fairly estimate the channel fading on each sub-carrier, and the estimation performance may not be affected because of relatively small amplitude of the signal on a sub-carrier.
At present, the method for allocating the CAZAC sequence for cells is as follows: the CAZAC sequence is allocated once with respect to each occupation mode of time-frequency resources of the sequence. Furthermore, when the occupation modes of the time-frequency resources of the CAZAC sequence to be allocated are the same in different cells, different CAZAC sequences having the same length and having small inter-sequence correlation value are allocated to the different cells. Thus, the signal interference between different cells is less. For example, as shown in FIG. 1, the occupation modes of the time-frequency resources of the sequence in cell A and cell B overlap each other totally, then CAZAC sequences having the same length are allocated for cell A and cell B respectively, where the two CAZAC sequences have low correlation, so that the signal interference between cell A and cell B may be avoided.